The present invention relates generally to a torque monitoring apparatus and, more particularly, to a torque monitoring apparatus adapted to be used for measuring the torque experienced by a device under dynamic loading conditions.
During the production and distribution of commercial products, a product unit may be exposed to external forces from a large number of sources. As a result, it may be difficult or impossible to determine which single external force or combination of external forces is responsible for creating a product defect. It is also difficult under such conditions to determine the nature and magnitude of the force(s) which have been exerted on a can body to cause a particular type of defect. For example, in the beverage industry, a beverage can, subsequent to its initial formation into a tubular can body having a bottom wall and an integrally formed sidewall with an open top, undergoes a number of operations performed by a variety of different machines. Typical operations include necking, flanging, filling, can end attachment, packaging, and automated machine transfer of can bodies between the various operating machines. It would be desirable to monitor various force related parameters experienced by can bodies as a result of these various processes to determine how various machinery or the can bodies themselves could be modified to prevent a particular type of damage, e.g. misformed end seams. However, prior to the present invention, such monitoring was impossible in view of the fact that a can body is in generally constant motion as it passes through an operating machine and in view of the restricted space environment within an operating machine. Such movement and space restriction prevent the attachment of a monitoring device and associated sensors and leads, etc., to a can body. A further problem associated with the monitoring of torque experienced by a beverage container is that it is unclear from the prior art how sensors could be mounted on a container to accurately measure torque experienced thereby.
A problem with measuring torque in a dynamic environment is also experienced with rotating machine components. For example, it would be generally desirable to be able to measure the torque experienced by the drive shaft of a truck under various operating conditions. Although torque on a shaft may be readily monitored under various static testing conditions, e.g. by applying a known force to the end of a known length moment arm attached to an end portion of the shaft, there was, prior to the present invention, no accurate method of determining the magnitude of a torque couple which is applied to a rotating shaft, say by an accelerating drive motor at one end and the associated inertial resistance of a transmission, etc., at the other end of the shaft. The rotation of the shaft prevents direct connection of any sensor mounted on the shaft to a data collection device such as a computer. Although electrical contact brushes might be used in association with shaft-mounted sensors, such brush contact, especially under widely-varying velocity conditions, is simply incapable of producing a high-resolution detection signal due to resistance variations between a brush and an associated contact ring. Furthermore, there is no known method for mounting strain gauges, etc., on a rotating shaft for accurately detecting torque experienced by the shaft. torque measurements derived from measured shaft angular velocity/acceleration and shaft moment of inertia are subject to error because of variables such as the friction in journals, etc., which are difficult to measure or predict and which may vary with velocity.